Condensing gases from electric furnaces.



fl. HECHENBLEIKNER. CONDENSING GASES FROM ELECTRIC FURNACES.

APPLICATION HLED FEB. no. 1911.

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connausruo cases Application filed February 10, 1917. ficrial Ito.M73611.

To all whom it may concern:-

Be it known that T, INGENUIN HEoErnN- BLEIKNER, a citizen of the UnitedStates, residing at Charlotte, in the county of Meek- ,lenburg and Stateof North Carolina-,have

invented certain new and useful Improvements in Condensing Gases fromElectric Furnaces, of which the following is a specification.

This invention relates to certain novel and useful, improvements in thetreatment of gases and has particular. application to a method ofcondensing gases produced 1n the manufacture of phosphoric acid by theelectric furnace process.

In the production of phosphorus from phosphatic material, such asphosphate rock, it is the practice to feed into the furnace a chargecomposed of the phosphate rock, preferabl in the form of calciumphosphate, a suita 1e flux, such as silica, and a carbonaceous material,such as carbon, charcoal or coke. The reaction which takes lace in theelectric furnace is represented y the following equation:

the oxidizable ases escaping in the form of carbon monoxi andphosphorus, the oxidization of such gases resultlng as follows:

sides phosphorus pentoxid, carbon dioxid,

nitrogen, and oxygen, large quantities of otherfgases and vapors derivedfrom the impurities in the rock. Besides dust from the rock, sand andcarbon there is produced silicon tetrafiuorid (SiF in appreciablequantities, as all mineral phosphate rocks contain calcium fluorid (CalFsometimes in amounts up to 10%. In the heat of the electric furnace thiscalcium fluorid is decomposed as follows:

4CaF +6SiO =QSiR-iiCaSiO, In my Patent No. 1,167,755 dated January 11,1916, I have set forth an apparatus and process 'for oxidizingphosphorus, so as toproduce a gas free from dust and at a sufficientlylow temperature to enable it to be easily treated for furthercondensation. After the gases leave the dust chamber of the apparatusshown in said patent, and which apparatus in its fundamental features isincorporated in the structure set forth herein, such gases, at a lowertemperature, contain mainly phosphorus pentoxid, carbon dioxid,nitrogen, oxygen and silicon fluorid. It is desirable to condense thesilicon fluorid aS well as the hosphorus pentoxid, as both of these noton y possess a commercial value, but are very injurious to surroundingvegetation and territory if set free in gaseous form into theatmosphere. The condensation of both these gases together may beaccomplished in scrubbing towers so that the resulting acid attained inthe condensation of the uses is a mixture of phosphoric acid (H 0 andhydrofluosilicic acid (H SiF and which product when utilized in themanufacture of fertilizer may be employed without separation into itscomponents.

In many instances, however, it is desirable to produce these two acidsseparately to obtain a commercially pure phosphoric acid or acommercially pure hydrofluosilicic acid, and this may be accomplished bythe method forming the subject matter of the present application.

In the present instance I propose to separate the phosphorus pentoxidsolids by electrostatic precipitation subsequently treating the residualgases to obtain the hydrofluosilicic acid.

It is a well known fact that fine mechanical dust as well as vapors suchas those of sulfur trioxid (S0,), phosphorus pentoxid (P 0 and sulfuricacid (H SO etc, may be precipitated electrostatically and consequently,by my present invention, in treatin gases issuing from the electricfurnace during the production of hosphoric acid as hereinbeforementioned? after such gases are freed from dust through the use ofsuitable apparatus such for instance as is shown in my Patent No.1,167,755, and cooled down to a temperature not injurious to thestandard apparatus used in the electric precipitator, I proceed toseparate the phosphorus pentox1d solids by electrostatic action whilethe residual gases containing silicon tetrafiuorid,

specification oi t tters Pa e; 7 Patenteda 34 1, was, i

in addition to nitrogen, oxygen and carbon dioxid are preferablysubjected to the action of water sprays in scrubbing towers to iveconcentrated hydrofluosilicic acid (H 81 according to the formula and inthis way the phosphorus pentoxid and the silicon tetrafluorid areseparately condensed and mixed with water to provide commercialhosphoric acid and hydrofluosilicic acid. he waste gases then remainingare free from harmful constituents and may be discharged into thesurrounding atmosphere.

The invention consists in the process set forth in and falling withinthe scope of the appended claims.

In the drawing the figure is a view partly in side elevation and partlyin section of one form of apparatus which may be employed in carryingout the process of the invention.

Referring now to the accompanying drawing in detail, the numeral 1indicates an electric furnace provided with the usual electrodes 2,while the feeding hopper for the carbonaceous material, such as coke, isindicated by the numeral 3'. Connected with the furnace 1 is an inclinedrotary kiln 4 having a feeding hopper 5 through which the phosphate rockand sand may be fed down the kiln into the furnace where it is broughtinto contact with the carbon or coke, within the heating zone of theelectrodes, the material passing down the kiln being preheated by thehot up-coming gases. The feed hopper 5communicates with a coupling pipe6 which connects the rotary kiln 4 with the dust or settling chamber 7,the latter having a vertical baflle wall 8 suitably located therein, asuitable cleanout door 9 being located at the bottom of the chamber. Theconstruction and operation of the apparatus thus far described is setforth in my Patent No. 1,167,755 hereinbefore mentioned. Instead,however, of attaching an exhaust fan directly to the dust chamber 7, apipe 10 leads from the upper end thereof and conducts the gas,practically freed from dust, to the electric precipitator 11. Thislatter, although it may be of any desired form, preferably comprises ashell which terminates in a hopper-like bottom 12 the lower end of whichis provided with a valve 13, which controls the passage of theprecipitated solids fIOm the bottom into the receptacle 14. The latteris intended to con tain water for taking up the solid or precipitatedphosphorus pentoxid, thus providing commercial hosphoric acid. Withinthe casing or she I of the precipitator are pipes of suitable materialsuch as metal or stoneware indicated at 15, through which pass the gasesto be subjected to the electrical treatment, while 16 indicateselectrodes inserted in these pipes and to which electrodes current issupplied through any suitable form of electrical conductor convenientlyindicated at 17. A connecting pipe 18 leads from the bottom of theprecipitator into the first scrubbing tower shown at T, in the firstinstance, there being two of such towers arranged in a series, thesecond tower being indicated at T. Of course any suitable number ftowers may be employed. Each tower embodies a support 19 arranged at thebottom of the tower casing 21, while 20 is the packing material for thedistribution of the gases and acids. From the upper portion of the towerT a gas conduit 22 leads to the bottom of the second tower T. Each toweris provided with an acid distributer 23, and with each acid distributeris connected a storage vessel 24. A pump 25 for circulating water andacid is connected with the bottom of each tower and from each towerthere leads a pumping line 26 discharging into one of the tanks 24. Anexhaust fan 27 is provided for drawing the gases from the electricfurnace through the condensing system and discharging the same into theatmosphere through the exhaust 28. The water supply line is indicatedconventionally at 29. The above is a brief description of the structuralfeatures of the apparatus shown in the drawings and the operationthereof is as follows: The charge of phosphate rock and sand is fedcontinuously through the hopper 5 into the rotary kiln 4 and passes downthe latter into the furnace, being preheated in its travel. Just beforeentering the furnace it is mixed with the carbonaceous material which isfed in through the hopper 3. After the gases are generated in thefurnace and properly oxidized through the admission of oxygengascs,preferably in the form of air, through suitable openings orpassageways 30, they pass through the rotary kiln, being cooled down inthe latter, a portion of the heat being absorbed by the down-comingcharge, and such gases then flow through the dust chamber 7 where theyare freed of dust and after passing around the battle 8 pass into theelectric precipitator through the pipe 10. In this precipitator thestream of gases is divided up into numerous small streams which passdown through the pipes 15 and while therein are sub ected to electricalaction through the electrode discharge. The solid phosphorus pentoxidwhich is thus electrically precipitated from the gases settles on thepipes 15 and from time. to time is deposited in the hopper bottom 12 ofthe precipitator from which it may be withdrawn through the valve 13 andtreated with water in the receptacle 14 thus producing commercialphosphoric acid.

As the gases leave the precipitator they are of course now free from thephosphorus pentoxid and pass through the conduit or pipe 18 into thescrubbing towers wherein they are treated on the counter-currentprinciple with water. That is to say, the gases flowing upward in thetowers" are treated with diluted acid or water flowing in the oppositedirection or down the tower, the gases passing through both theabsorption or scrubbing towers to give a complete absorption. The morediluted acid from the second tower is sprayed and circulated in thefirst tower while in such second tower water is added to the absorptionsystem through the pipe line carrier 29 and circulated to give a dilutedacid which is subsequently pumped into the first absorption tower andconcentrated through the heat of the gases. Thus a complete absorptionof the silicon tetrafluorid (SiF is had and at the same time thehydrofluosilicic acid resulting is of a commercial concentration.

To obtain the best results in practice the gases flowing from the kilnto the dust chamber while having a relatively low temperature should notbe cooled to such an extent as to cause the precipitation of thephosphorus pentoxid as a solid with the dust in such chamber but thepentoxid should be maintained at such temperature as will insure itremaining vaporized while it enters the precipitator.

vVhile I have herein shown and described the preferred embodiment of theinvention, I wish it to be understood that I do not limit myself to allthe precise details herein set forth by way of illustration asmodification and variation may be made without departing from the spiritof the invention or exceeding the scope of the appended clalms.

What I claim is: a

1. The herein described method of treating gases containing phosphoruspentoxid and silicon fluorid, to separately produce phosphoric acid andhydrofluosilicic acid, which consists in electrically precipitating thephosphorus pentoxid as a solid and bringing said solid into contact withwater to form phosphoric acid, and then passing the residual gasescontaining the silicon fluorid through an absorption system in contactwith water to convert the silicon fluorid into hydrofluosilicic acid.

2. The herein described method of treat ing gases containing phosphoruspentoxid and silicon fiuorid which consists in electricallyprecipitating the phosphorus pentoxid as a solid and subsequentlyremoving the silicon fluorid by passing the residual gases containingthe same in contact with water flowing in a direction opposed to theflow of the residual gases.

3. The herein described process of treating gases which consists insubjecting gases to the action of an electric precipitator toprecipitate as a solid certain components of the gas and subsequentlypassing the residual gases through an absorption system operating on thecounter-current principle.

4. The herein described method of treating gases containing phosphoruspentoxid and silicon fluorid which consists in precipitating thephosphorus pentoxid through electrical action and subsequently scrubbingthedresultant gases to obtain hydrofluosilicic acl 5. A step in the artof precipitating phosphoric acid comprising electrically precipitatingphosphorus pentoxid as a solid from gases containing such phosphoruspentoxid and subsequently bringing such. phosphorus pentoxid in contactwith water to form phosphoric acid.

6. A step in the art of precipitating phosphoric acid which comprisespreliminarily removing dust from the heated gases containing phosphoruspentoxid, and subsequently subjecting said heated gases to electricalprecipitation to precipitate the phosphorus pentoxid as a solid and thenbringing said solid into contact with water to form phosphoric acid.

7. The herein described method of treating gases containing phosphoruspentoxid and silicon fluorid which consists in preliminarily removingdust from the gases while the latter are in a heated state, subjectingthe gases so cleaned to electrical precipitation to precipitate thephosphorus pentoxid as a solid, then subjecting the residual gases toabsorption and then concentrating the resultant acid. V

8. The herein described method of treating gases containing phosphoruspentoxid and silicon fluorid which consists in electricallyprecipitating the silicon fluorid and subsequently removing the siliconfluorid by passing the residual gases containing the same through anabsorption and concentrating system operating on the counter-currentprinciple.

In testimony whereof I affix my signature.

INGENUIN HECHENBLEIKNER.

